Science Artificial Gravity

maybe like a cat in washing machine :lol:


Who put a cat in a washing machine?! And why didn't I think of that?!

---------- Post added at 11:46 ---------- Previous post was at 11:42 ----------

I would actually like to see the math behind the propellant requirements for this. Low thrust but high efficiency thrusters (like ion drives or even arcjets) are probably the answer.


Alright, I can whip that up...

---------- Post added at 11:57 ---------- Previous post was at 11:46 ----------

Ok, here we go. I've dumbed down the thing.

First of all, I'm assuming you'll be using some high Isp, low thrust thrusters, where the mass of the propellant that will be shed is much much smaller then the mass of the ring you're trying to spin up.

Second, I've assumed all of the mass of the ring is concentrated at the radius r. That's not entirely accurate - I'm neglecting the body and the supports that need to be used to hold the ring together. Also, since I'm not in the mood of designing the whole ship, I won't do any detailed study of it's geometry...


Assuming that, here it is:

Going with rigid body mechanics, J*dw = M*dt, where J = m*r^2 (remember, all of the mass is concentrated in the wheel), w is the angular velocity, M is torque, t is time and mass of the ring is marked as m.

M = F * r, where F is the thrust of the ion engines and r the radius it's mounted at. I'm assuming that to be the same radius as the ring.

So, time you need your engines to be active can be expressed as:

t = J*w/M = m*r^2*w/(r*F) = m*r*w/F.

t = m*r*w/F

So, given that your ion engine has a pretty constant mass flow O, the expended propellant can be given as:

mp = O * t = O*m*r*w/F

So here it is:

mp = O*m*r*w/F
 
No, he only put a cat in a box with a single radioactive atom and a detector that would pick up the decay and break open a capsule of cyanide and to highlight the absurdity of an early assumption of Quantum theory that since the atom would be in an undetermined state until an observer measured it, the cat would also be dead and alive at the same time.

That ain't that bad...


I like this one:

And this one:
 
In case you mean that you still follow a curved path if you jump up, I think you are wrong. Mass does not follow a curved path without centripetal force. As soon as you jump up, you are actually weightless again until you hit the ground which forces you to follow the curved path of rotation. Depending on your jump, and the size and shape of the station, you might even hit the ceiling first and lose control, maybe like a cat in washing machine :lol:

You're still spinning with the centrifuge, you are not stationary. As jedidia said, you will eventually fall to the floor.

And cats in washing machines? That's cruel... :uhh:

And the smaller the station, the smaller the comfort due to high rotaion, if you want to maintain 1g. If it is only 10 meters in diameter, which already is a lot, you won't feel fine anymore. Even 100 meters of diameter will be still pretty uncomfortable.

At 5 meters in radius (to produce 1 g) the angular velocity will probably be too much to bear. At 50 meters, you get a little overr 4 rpm. Which some studies suggest is livable (although one would need some time to acclimatise), especially if your crew is unsusceptible to motion sickness.

You can also reduce the amount of centripetal acceleration. While there may be some degeneration in the crew, it would certainly be better than months or years in zero g. Ongoing research is needed to study the effects of partial G in humans.

A feather even more, and a human body certainly less ;)

With the speed of the centrifuge you calculated, I think a human would be pushed along by the wind quite well.

Now, the air inside would have to be synchronised with the centrifuge. Which would inevitably happen from friction with the inside, although thin baffles (made of thin plastic, say) could help this along. If you are spinning a module instead of a ring, the air will have nowhere to go but be pushed by the wall behind it.

I don't think that something like ion drives are the answer to introduce a rotation of a station which consitst of thousands of tons of mass. Also, the station doesn't only has to rotate, it should also leave earth orbit to begin its journey ;)

Why can't a propulsion system such as an ion drive or an arcjet have this capability? They may be low thrust, but long burn times can be dealt with.

Such a spinning spacecraft also does not need to be thousands of tons in mass. A simple centrifuge made of, say, two TransHab modules connected by a pretty fancy pressurised tunnel, might mass less than 80 tons (excluding things like radiation shielding, which will also push up structural mass). Two modules swinging around each other (or a module swinging around a common axis with the drive portion of the spacecraft) on a tether would probably mass much less, and could have a larger radius (lower angular velocity), though you will not be able to transfer to the other module through a tether...

A system bound by a tether also has to be robust, and so certainly won't be "very light" anymore.

Structures in tension can be lighter than structures in compression. Many heavy objects are often suspended by cables.

The cable could be made out of some sort of aramid, perhaps. Or even carbon fibre. There would have to be electrical connections through the cable for communications and power, but these need not be prohibitively massive.

The "spinning on a string" concept has been tested on a Gemini flight, although the angular velocity was not high enough to create noticable gravity.

Which is why I wrote that we have to revolutionize our propulsion technologies. If we manage to reach Mars within 2-3 weeks, the crew will be just fine. No rotatinal pipe dream required. But traveling to Mars within 2-3 weeks also is a pipe dream because the next issue would be a tremendous acceleration. You want to do it slowly? Maybe this would increase the travel time already significantly...

See the study that is being done right now with things like VASIMR. You do not need high accelerations; VASIMR does Mars in perhaps around a month. It accelerates and decelerates slowly, but does so throughout the entire journey.

Higher accelerations might be needed for faster travel times, but this impacts on engine design, not whether the crew can handle it. It is not tremendous in terms of multiple Gs. Fusion propulsion may be an answer to high thrusts at high specific impulses, but it is pretty far off technologically. Even some forms of fission propulsion may be able to yield dramatically shortened travel times.

And in agreement with the theory of relativity, all observations do show that particles and information can't be faster than light.

Particles with a rest mass can't accelerate to (or beyond, obviously) c. But general relativity does allow for apparent FTL, such as wormholes.

Whether information as a whole can go FTL is the big question, because if not it rules out FTL altogether. Experimental evidence shows that quantum-non local connection for example has a speed several times that of light, but cannot be used for transmitting information unless used in conjunction with another communication system.

Erwin Schroedinger? He was pretty nasty to cats.

At least his cats were alive and dead until you observed them...
 
Gosh... science is so unforgiving...



actually it's not... most of what we know about stuff started out at some point as educated guessing and trial-and-error...

trust me, if science was indeed unforgiving, we'd be screwed as bad as a cat in a washing machine by now :lol:


so feel free to make mistakes, it's what makes us (some of us, at least) human




but as far as gravity rings go, they would impose a structural challenge on the ship design... an easier approach would be to simply spin the whole ship...

but if you MUST have a ring... i'd suggest that the airlocks, and pretty much everything that requires sealing be disconnected while the ring is spinning, and connect only when it's stopped, to minimize the "moving parts" problem


and why does it NEED to be a ring anyways? it's such a hard structure to put together in orbit... what if instead, you had something shaped like a handlebar?... it's much easier to build....


an long-haul vessel doesn't necessarily need to have constant gravity throughout it's whole manned deck... you could have the crew quarters and recreation modules on the centrifuge, but assuming crew members would take submarine-like work-rec-sleep shifts, 8 hours a day in zero g can't be all that bad for you, right?
 
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you may or may not land in exactly the same spot, but it would probably be almost like jumping here on earth. maybe a inch different? maybe exactly the same. the space shuttle moving is NOTHING like a centripetal force ring. that might be something like what would be happening in the middle.

if you want to experience centrifuge induced g-forces, go to your local state fair and ride a gravitron!
 

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unless you do not live in united state :thumbup:
 
and why does it NEED to be a ring anyways? it's such a hard structure to put together in orbit... what if instead, you had something shaped like a handlebar?... it's much easier to build....

well you either need to have 2 on either side of the ship, or a large counterweight to balence it out.

The "handle bar" would also need to be curved, as you would get uneven centrifugal force from a straight object since for the radius to the pivot point to remain constant, your hab module needs to curve around it.

so you have a curved hab, with a identicle hab on the other side of the ship - why not just fill in the gaps and make it one big ring?
 
but it would probably be almost like jumping here on earth. maybe a inch different?

The main difference is that your upward momentum doesn't get reduced by gravitational pull. You jump straight up at a speed of 1m/s, that speed will NOT diminish, as it would on earth. The only thing that gets you back to the ground is that you still got your forward momentum from the spin, that will carry you forward until you meet the ring again because it intersects your trajectory.

It would be very easy jumping to the ceiling, even if the room is three meters high. It will be easier the bigger the radius of the centrifuge is. At least if I pictured the whole thing correctly in my head.
 
well you either need to have 2 on either side of the ship, or a large counterweight to balence it out.

The "handle bar" would also need to be curved, as you would get uneven centrifugal force from a straight object since for the radius to the pivot point to remain constant, your hab module needs to curve around it.

so you have a curved hab, with a identicle hab on the other side of the ship - why not just fill in the gaps and make it one big ring?

ah, perhaps i fail to properly paint this picture...

the "handlebars" would be parallel to the rotation axis.... think of a ship shaped like the letter H, spinning "vertically"... you wouldn't need a curved deck then, and still have plenty of space on the decks on either side :thumbup:

its a much more practical concept for building in orbit:cheers:
 
The main difference is that your upward momentum doesn't get reduced by gravitational pull. You jump straight up at a speed of 1m/s, that speed will NOT diminish, as it would on earth. The only thing that gets you back to the ground is that you still got your forward momentum from the spin, that will carry you forward until you meet the ring again because it intersects your trajectory.

It would be very easy jumping to the ceiling, even if the room is three meters high. It will be easier the bigger the radius of the centrifuge is. At least if I pictured the whole thing correctly in my head.

In my understanding, it depends on BOTH the radius of the centrifuge and the angular velocity/RPM of the centrifuge. You could adjust the parameters (within a certain human comfort range) to get various effects. That Page I linked to above has some nice diagrams and information about artificial gravity, answering several of the questions that have been posed since I posted it. (Perhaps I should have been more specific when I first posted that, sorry.)
 
well you either need to have 2 on either side of the ship, or a large counterweight to balence it out.

The "handle bar" would also need to be curved, as you would get uneven centrifugal force from a straight object since for the radius to the pivot point to remain constant, your hab module needs to curve around it.

so you have a curved hab, with a identicle hab on the other side of the ship - why not just fill in the gaps and make it one big ring?


why not? because if it's radius is 1km then "filling in the gaps" makes what could be small, like 2 hab modules at the end of the already large 2km structure in the middle which could range in complexity but more than likely would be very minimalistic, to making over 6km of living space? Sure, but thats becoming more of a space colony than a vessel! Although for the large trip maybe that is what would be needed. I think each type has it's own use.

jedidia said:
The main difference is that your upward momentum doesn't get reduced by gravitational pull. You jump straight up at a speed of 1m/s, that speed will NOT diminish, as it would on earth. The only thing that gets you back to the ground is that you still got your forward momentum from the spin, that will carry you forward until you meet the ring again because it intersects your trajectory.

It would be very easy jumping to the ceiling, even if the room is three meters high. It will be easier the bigger the radius of the centrifuge is. At least if I pictured the whole thing correctly in my head.

And the main difference between what you picture and the actual ring is that the forward momentum from the spin is huge. For one g of the kilometer ring I calculated slightly over 98m/s

The curvature, or rise from the jumper's perspective, of the ring is what emulates the reduction of vertical speed on earth.

the problem with picturing things in your head is that it's a guess with no solid foundation.

In the graphic I posted, I used the generous jumping velocity of 3.8 m/s. While they would have traveled over 78 meters from where they started (in an onlookers perspective), they would have reached a maximum distance of only 79 cm from the ground and land very close to where they jumped.

the REAL main difference is there would be small variations that would mess with your equilibrium and balance. I think someone posted an article about it earlier. Also the floor would be at a slightly different angle than when you jumped.

---------- Post added at 09:07 AM ---------- Previous post was at 09:04 AM ----------

yes it was spike's article i was talking about has some in depth discussion about the small variations that I was referring too.
 
A radius of 1 Killometer seems way to huge - using the spin calc refered to earlier a hab with a radius of 50 meters would only need to spin at 4 RPM to maintain 1G when a radius of 1km would still need to rotate at just under 1 RPM

the only true advantage to using a very large radius as you say i guess would be for the reason you just posted, the floor will come up from under you at a different angle.
at 4rpm, you would rotate with the hab 360 Degrees in 15 seconds - a jump lasting 1 second would mean that the ground will meet your feet at (1/15)*360 = 24 degrees, your angular momentum would cancel out this effect to some extent - how much i have no idea, think about when you cancel prograde and dont click kill rot in orbiter, you still maintain prograde for a while until other perturbations pull you off.

at 1km at 0.94 rpm - 64 seconds per rotation.
a 1 seconds jump, (1/64)*360 = 5.6 degrees, which im sure your angular momentum would to cancel out.

i dont however think that an extension length by a factor of 20 is worth a reduction in rpm by a factor of 4 or would have a huge effect on comfort as described above.
 
Oh yeah personally I think that a radius of 1km is impractical... at least right now. I was working with that specific scenario because the people were discussing a space ring with a radius of 1km. I agree that a 50 meter device seems more plausible for current space travel. Besides, I think that even if there were weird effects to your equilibrium, the astronauts would get used to it the same way that ocean-going folks get their "sea legs." I speculate that a returning astronaut would feel lightly disoriented when returning to the Earth! :lol:
 
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